The field of the present invention is that of pyrotechnic triggers, namely components allowing a pyrotechnic effect to be transmitted to a pyrotechnic chain.
Triggers used in the armaments sector are already known. In general they consist of a metal cell into which a pyrotechnic substance is pressed. French Patents FR 2,506,927, FR 2,513,751, and FR 2,538,094 describe such triggers. Although these devices are reliable, they suffer from high production cost.
The cell is made of relatively thin metal and must be closed by a metal barrier designed to break under the pressure generated by the pyrotechnic substance. The barrier is itself coated with varnish to ensure a seal against environmental moisture.
Production of such a cell is expensive as it requires a number of delicate operations. In the case of triggering by electric current, the electrodes are mounted on an insulating base, usually made of sintered glass or ceramic. This base is fragile and fairly expensive to manufacture. In addition, the cell itself must be installed inside a supporting housing that will carry the electrical connectors and allow the trigger to be installed in the pyrotechnic chain.
As a result, the triggers of the prior art are unsuitable for large scale production at low cost, as industry requires.
U.S. Pat. Nos. 2,968,985, 2,767,655, and 4,819,560 teach triggers having housings made of plastic. These inexpensive triggers are designed in particular to trigger explosive cartridges used in the mining or quarrying industry. They generally have a housing of constant thickness that contains the trigger charge and that is fragmented when the trigger charge is triggered.
Such trigger, however, does not allow the size of the housing fragments obtained to be controlled, which is a drawback for application to technical areas other than quarrying, for example in the armaments industry or the safety systems industry.
U.S. Pat. No. 4,576,094 describes a plastic trigger for a missile propulsion unit that has a thin cylindrical wall that is fragmented when triggered. The goal is to prevent the missile nozzle from becoming clogged with the trigger residues. This trigger, however, is expensive to manufacture as it requires extremely thin cylindrical parts to be manufactured and then to be assembled after filling with a sensitive pyrotechnic composition. In addition, the thinness of its envelope renders it fragile so that it is difficult to use in areas where mechanical constraints (impacts, vibrations) are considerable (armaments, automobile safety). Moreover, the thinness of the envelope does not allow the pyrotechnic composition to be sufficiently contained. Finally, its thin envelope is surmounted by a solid lid that could jam or disrupt the pyrotechnic systems it is supposed to trigger.